Asymmetric Link Delay Measurement via Variable Packet Sizes
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Solution Overview
Problem
Existing methods for time synchronization in packet-oriented communication networks, such as those using the Precision Time Protocol (PTP), fail to accurately determine one-way delay over asymmetric links, where uplink and downlink bandwidths differ, as they assume equal link speeds, which is not valid for links like xDSL lines.
Innovation Solution
A method involving nodes exchanging packets of different sizes to measure round-trip times, allowing for the calculation of asymmetric link bandwidths and delays by eliminating handling delays and using these measurements to determine specific link path delays and bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RTT measurement is used to determine one-way delay, then time synchronization can be achieved, but accuracy deteriorates on asymmetric links where uplink and downlink bandwidths differ
Solution Approach 1:
The patent segments the RTT measurement into two separate one-way measurements by using packets of different sizes. The first packet size measurement gives one direction's delay, and the second packet size measurement gives the reverse direction's delay. This segmentation allows accurate determination of one-way delays even on asymmetric links where traditional RTT/2 assumption fails.
Solution Approach 2:
The patent changes the packet size parameter between measurements to exploit the asymmetric bandwidth characteristics. By sending packets of different sizes in opposite directions and measuring the resulting RTT differences, the method can calculate separate one-way delays for each direction, adapting to the asymmetric link conditions rather than assuming symmetry.
2Device complexity
If equal link speeds are assumed for simplification, then calculation is easier, but measurement precision deteriorates on asymmetric connections
Solution Approach 1:
The patent introduces dynamic measurements by exchanging packets of different sizes in both directions and calculating separate one-way delays for each direction. This dynamic approach replaces the static assumption of equal link speeds with actual measured values that adapt to the specific asymmetric conditions of the connection, thereby improving precision without requiring overly complex manual configurations.
3Reliability
If traditional PTP is used on asymmetric links, then time synchronization is attempted, but accuracy deteriorates due to inability to determine actual one-way delay
Solution Approach 1:
The patent implements a feedback mechanism where the measured RTT values from packet exchanges are used to calculate and compensate for asymmetric one-way delays. The system continuously measures the actual transmission times in both directions and uses this feedback information to correct the time synchronization calculations, thereby maintaining reliable synchronization with high accuracy even on asymmetric links.
Data Source
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AI summary
A method and a device for processing data on a connection between two nodes of a communication network are provided, wherein the first node conveys first data of a first size to the second node; wherein the second node conveys second data of a second size to the first node; wherein the first node determines a first time based on a duration from the first data being sent until the second data is received; wherein the first node conveys third data of the second size to the second node; wherein the second node conveys fourth data of the first size to the first node; and wherein the first node determines a second time based on a duration from the third data being sent until the fourth data is received. Also, a communication system comprising at least one such device is suggested.